In recent years, an image formation process of an electrophotographic system has been adopted in a production printing (PP) market. In the image formation process, a plate for printing is not required, so that the necessary number of printed sheets can be formed on demand. Further, in order to improve image quality and durability, a varnish, is applied to an image to form a varnish coating film (hereinafter may also be referred to as “varnish layer”) in the PP market. Requirements for application of a varnish to a toner image formed by the image formation process of an electrophotographic system or an image obtained by heat-fixing the toner image (hereinafter may also be collectively referred to as “fixed image”) have also increased.
However, the fixed image obtained by the image formation process of an electrophotographic system has problems such as varnish repellent due to its low varnish application property. Furthermore, even when the varnish can be applied, the fixed image has problems such as deterioration of adhesion to a varnish layer.
Such problems may be caused by a wax bleed-out to the surface of the fixed image due to heat-fixing or exposed on the surface of the toner image due to the configuration of toner particles. In order to solve the problems, use of a polar wax as a parting agent to improve the wetting property of a varnish and the varnish application property has been proposed (see Patent Literatures 1 and 2).
However, the varnish application property may not be sufficiently imparted to a fixed image obtained by the use of the polar wax.
Furthermore, the kind of used wax is restricted, so that the degree of freedom of selection of wax is low.